EFFECTS OF SUBSTRATES ON MAXIMAL AEROBIC WORK AND OXYGEN-CONSUMPTION OF THE RAT AND GUINEA-PIG HEARTS

Isolated rat hearts perfused by Krebs solution supplemented with gluco se reacted to a rise in resistance with twofold increase in work (card iac output times aortic pressure). Contrary to rat hearts those of gui nea-pigs failed to react to increased resistance by significant increa se in work. Addition of insulin and pyruvate to perfusate of guinea-pi g hearts increased initial level of heart work but not its increment i n response to rise in resistance. Oxygen consumption correlated closel y with aortic pressure heart rate product. When Insulin and glucose we re used oxygen consumption at equal pressure-rate products was approxi mately equal in hearts of both species. In experiments on rat hearts a ddition to perfusate of pyruvate and especially of octonoate (both wit h insulin) was followed by increment in increase of oxygen consumption but not of heart work. Results of this study allow to assume that dif ferences between rats and guinea-pigs In dynamics of heart work in res ponse to increased resistance can hardly be explained by decreased aer obic capacity of guinea-pig hearts. It is more probable that they are caused by differences in calcium transport in cardiomyocytes.